Baltic J. Modern Computing, Vol. 7 (2019), No. 1, 151-170 https://doi.org/10.22364/bjmc.2019.7.1.11 Geodynamic Hazard Factors of Latvia: Experimental Data and Computational Analysis Valērijs ŅIKUĻINS Latvian Environment, Geology and Meteorology Centre, Maskavas Str. 165, Riga, Latvia University of Latvia, Faculty of Geography and Earth Sciences, Jelgavas Str. 1, Riga, Latvia [email protected]Abstract. Geodynamic hazards of Latvia were identified by experimental and computational methods, including tectonophysical modeling in the MathLab environment. Among these factors are seismic shocks in Riga on November 22, 2010, abnormally high velocity of displacement of opposite sides of the Cirulisi fault, an increased anomaly of radon concentration on the profile crossing Olaine-Incukalns fault, deformations of buildings in the tectonic zone, formed by Olaine- Incukalns and Bergi faults. An analysis of the isostatic equilibrium of the Earth's crust at the Moho discontinuity level allowed to estimate Earth's crust development's and tendency type. On the basis of the analysis of experimental data and the results of tectonophysical modeling, a depression site was discovered in the area at the Plavinas dam. The conclusion is made about the expediency of geodynamic monitoring in areas of large agglomerations (Riga) and especially responsible objects (Plavinas dam, Incukalns underground gas storage). Key words: geodynamics, seismotectonics, Earth's crust, isostatic index, tectonophysical modeling, Persistent Scatterer Interferometry. 1. Introduction The main factors determining the geodynamic activity of a particular territory are the following: 1) proximity to the boundaries of tectonic plates; 2) the type of the boundary between tectonic plates; 3) geological situation (platform, geosyncline area); 4) the influence of exogenous factors (glacial load) and the reaction of Earth's geospheres (restoration of isostatic equilibrium); 5) the orientation of the maximum horizontal compressive stresses. The territory of Latvia is located in the north-west of the ancient, Precambrian East European craton (EEC). In the west-southwest the EEC borders on the younger and more active Phanerozoic orogen of Western Europe (POWE). The border between platforms is the Teisseyre-Tornquist zone, from which Latvia is located at a distance of about 375 km. The distance to the nearest divergent boundary located in the North Atlantic (DBNA) is about 1840 km, and to the nearest convergent boundary located in the Mediterranean Sea (CBMS) - about 1870 km. The divergent boundary it is constructive boundary where two tectonic plates are moving away from each other and new crust is
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Baltic J. Modern Computing, Vol. 7 (2019), No. 1, 151-170
https://doi.org/10.22364/bjmc.2019.7.1.11
Geodynamic Hazard Factors of Latvia:
Experimental Data and Computational Analysis
Valērijs ŅIKUĻINS
Latvian Environment, Geology and Meteorology Centre, Maskavas Str. 165, Riga, Latvia
University of Latvia, Faculty of Geography and Earth Sciences, Jelgavas Str. 1, Riga, Latvia
At the anomalous area, the Moho discontinuity is located at a depth of 57 - 59 km
(Figure 4), i.e. deeper than the average depth of 44 - 45 km of the Moho discontinuity for
the EBR. The DSS profile passed along the north-north-western border of the Vidzeme
Upland. On this section of the Vidzeme Upland, the terrain is characterized by an
elevated surface with elevations of up to 200 m, while the lowland, located to the north-
west has average marks of about 100 m.
Thus, the tendency of the development of the Earth's crust between the pickets 375 -
410 (Ieriki in Figure 1) corresponds to the II type of Earth’s crust development. In this
case the leading process is stipulates motion of Moho boundary down and motion of
Earth's surface up, consequently moving of these boundaries go in opposite directions.
So the isostatic index is positive.
Comparison of the isostatic index ∆𝑚 with geological-geophysical and deformation
parameters showed its close connection with the velocities of modern vertical
movements 𝑉𝑉 for the Latvian territory, as well as the coincidence with the maximum
values of amplitude of neotectonic movements 𝐴𝑁 and local maximum of the heat flow
𝑄 (Figure 4). Neotectonic and modern uplifts indicate the inherited and positive
character of the Earth's crust movement in this region.
The largest underground gas storage in Incukalns and transport infrastructure of the
Rail Baltica railway are located (Figure 1) in the immediate vicinity of the section of the
Earth's crust with the II type of its development and an abnormal rate of elevation in
Ieriki area.
Seismic shocks in Riga and the Riga region November 22, 2010
Macroseismic studies have shown that three points (points 1 to 3 at Figure 5) in
which shocks were felt are located in the north-west of Riga, in the districts of Ilguciems,
Kurzeme Avenue and Ulmana alley. In some of these points, the shock was felt much
later than the average time (~ 12 hours) noted at other points. The four points in which
the shock was felt are located in the tectonic zone formed by the Olaine-Incukalns and
Bergi faults (points 4-7 at Figure 5). The intensity of tremors is estimated as II - III
degree on the EMS-98 scale.
The Olaine-Incukalns fault is the longest fault of Latvia, stretching more than 130 km
from the south-west to the northeast, and in the Cesis area, changing its direction to the
east, towards Pskov. This fault, unlike other tectonic faults, was better studied, in
connection with the creation of an underground gas storage facility adjacent to it in the
Ragana area. The Olaine-Incukalns fault is the predominant thrust mechanism with a
strike-slip component, while most other faults in Latvia are normal faults (Brangulis and
Kanevs, 2002) or prevailing normal fault with strike-slip component. According to eyewitnesses, a change in the color of the Kalkugrvas water sources of
the Allazi district was noted (point 8). In one of the questionnaires, the respondent noted
a change in the properties of the spring water ("the water became a bit yellowish") a day
before the shock, i.e. November 21. Kalkugravas water springs are located about 9 km
from the Olaine-Incukalns fault and 4.5 km from the Kekava fault. Numerous studies
indicate that changes in hydrogeochemical parameters can occur before earthquakes
(Claesson et al., 2004; Barberio et al., 2017; Chaudhuri et al., 2013). However, these
changes were characteristic of earthquakes with a magnitude greater than 5.5.However,
great importance is the distance from the source of the earthquake to the place where the
change in hydrogeochemical parameters was noted. According to studies of the
relationship between the magnitude of the earthquake and the precursor's occurrence, an
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earthquake's precursors with a minimum magnitude of 3.5 to 3.6 appears 7 to 8 days
before the earthquake (Chaudhuri et al., 2013).
Fig. 5. Seismic shocks in Riga and the Riga region on November 22, 2010, Persistent Scatterer
points on the Cirulisi fault and the profile of the radon concentration observation points crossing
the Olaine-Incukalns fault. Designations: 1 - points in which shocks were felt within of zone
formed by the Olaine-Incukalns and Bergi faults; 2 - points in which shocks were felt in other
parts of Riga; 3 - tectonic faults in the Caledonian structural complex; 4 - the Kalkugravas water
spring; 5-Persistent Scatterer points on the Cirulisi fault; 6 - points of measurement of radon
anomaly; 7 - radon survey profile. The sidebar shows points 14 and 15 on opposite sides of the
Cirulisi fault.
Modern vertical movements
Using the Persistent Scatterer Interferometry method (PanGeo Project), an
anomalous velocity of points 14 and 15 (Figure 5, on the tab) located on opposite sides
of the Cirulisi fault was found at a distance of about 80 m from each other (Nikulins,
2017). These points move in opposite directions (Figure 6) at velocities of − 11.6
mm/year (point 14, IP = 62392) and + 13.8 mm/year (point 15, IP = 62371), whereas an
average background velocity in Riga of ± 1.5 mm/year (Nikulin, 2014).
The contrasting motions of these points on different sides of the Cirulisi fault
indicate its geodynamic activation. The length of the Cirulisi fault is only 13 km and on
the northeast edge it adjoins to the Olaine-Incukalns fault. At a length of about 9 km,
between Valdlauci and Stunisi, there is a powerful tectonic node formed by Dobele-
Babite, Cirulisi, Olaine-Incukans, Sauriesi and Bergi faults.
The Cirulisi fault's northern side is raised whereas southern side is lowered, that
indicates the thrust fault regime, due to pressure from the North Atlantic to the southeast.
Geodynamic Hazard Factors of Latvia 161
Earlier it was already noted (Brangulis et al., 1984) that thrust regime is characteristic of
the mechanism of the Olaine-Incukalns fault. Indirect confirmation of the thrust regime
are the heights of two points located on the southwestern wing of opposite sides of the
Cirulisi fault, at a distance of 1390 m between the points. The northern point has a height
mark of 16.4 m, whereas the southern point is 10.4 m. The difference between elevations
is slightly more than 6 m.
Fig. 6. Vertical displacements of PS points 62371 and 62392, located on different sides of the
Cirulisi fault. The abscissa indicates the number of days since the beginning of the research on
August 8, 1992.
The Cirulisi fault may have a small strike-slip component, however, there is no
complete clarity in the relation of the type of this strike-slip. The azimuth of the
maximum horizontal compression stress 𝑆𝐻𝑚𝑎𝑥 , determined on the basis of the decision
of the focal mechanism of the first Kaliningrad earthquake on September 21, 2004
(11:05:03 GMT) is 166°, and on the basis of the decision of the focal mechanism of the
second Kaliningrad earthquake (13:32:31 GMT) is equal 157° (Heidbach et al., 2016). In
these cases, the Cirulisi fault will have a small left-lateral strike-slip component. Thus,
the Cirulisi fault is prevailing thrust fault with a small strike-slip component. At the
same time, the direction 𝑆𝐻𝑚𝑎𝑥 may differ from the values of the Kaliningrad earthquake
sources obtained as a result of the decision of the focal mechanism. If the azimuth 𝑆𝐻𝑚𝑎𝑥
is less than 147°, then a right-lateral strike-slip component may appear in the thrust
regime. This can affect the change in the geodynamic situation, contributing to the
growth of tectonic stress in the area of the aforementioned tectonic node.
Anomalies of radon concentration in the surface air
The geodynamic activity of the Olaine-Incukalns fault was confirmed by the
anomalous concentration of radon detected on the profile at the Sigulda area (Fig. 5).
One of the three test sites for investigation of anomalous concentration of radon was
located here. In accordance with the results of studies of the subsurface radon
concentration in Latvia based on the report of Gilucis in 2014, at the Sigulda site, an
162 Ņikuļins
anomaly of increased radon concentration was detected at point number 12 (Figure 7)
(Ņikuļins, 2017a). Its value reached about 140 KBq/m3, which exceeds the concentration
of radon at the neighboring observation points in 1.6 - 3 times.
The Olaine-Incukalns fault intersects the section between points 13 and 12, about 1
km long (Figure 5). These points are located on different sides of the Olaine-Incukalns
fault. It is known that radon is an indicator of the continuity of the geological
environment, the presence of faults and their activity (Spivak, 2014; Ge et al., 2014).
Moreover, radon is considered as one of the possible precursors of earthquakes (Ge et
al., 2014; Pulinets et al., 2015; Gregoričetal., 2012). A higher background level and
bursts of high radon values are associated with an increase in voltage in the medium
[Chyi et al., 2005].
Fig. 7. Change in subsurface radon concentration along the profile crossing the Olaine-Incukalns